In many amplifier applications, the amplifier drives a capacitive load or a load that is substantially capacitive. In some applications, such as successive approximation register (SAR) analog to digital converter (ADC) drivers, which include amplifiers, a resistor/capacitor (RC) filter is typically required at the output of the amplifier. The SAR ADC has an internal sampling capacitor, wherein the filter typically requires an output capacitor that is much larger than the sampling capacitor. Accordingly, the amplifier sees this larger output capacitor. In some situations, the value of the output capacitor can be as much as twenty times larger than the value of the sampling capacitor. In applications such as SAR ADCs, where the amplifier directly drives capacitive loads, the large output capacitance results in a phase shift at the output of the amplifier, which causes the amplifier to be unstable.
In addition to the stability issues, when the output load is substantially capacitive, the output stage of the amplifier typically has to expend a significant amount of power in order to operate the amplifier over a usable bandwidth, which reduces the efficiency of the amplifier.